Microwave-assisted separations using volatiles

ABSTRACT

The generation of volatiles from liquid or solid materials is enhanced and accelerated by exposure to microwave radiation. Normally the energy transfer is effected preferentially toward the liquid or solid materials over the generated gaseous volatiles. Sufficient energy is provided at a selected rate that enhances the generation of volatiles to effect removal as vapor or to produce a pressurized vapor phase. Flow-through separations from a matrix having a microwave-absorbing liquid component are conducted by exposing to microwave radiation to vaporize this component and processing the vapor either by flowing through a selective permeable membrane, or by enclosing the vapor and matrix in a confined space and flowing matrix through a selected separation medium, and recovering residual matrix. These separations are particularly useful in analysis contexts.

This application is a division of application No. 08/653,553, filed May4, 1996, (now pending). This is a continuation-in-part application ofU.S. Ser. No. 08/327,638 filed Oct. 24, 1994, (now U.S. Pat. No.5,519,947 issued May 28, 1996), which is in turn a continuation-in-partof application No. 08/012,475, filed Feb. 2, 1993, now U.S. Pat. No.5,377,426 issued Jan. 3, 1995.

FIELD OF THE INVENTION

This invention relates to a method of generating volatile compounds froma variety of matrices containing volatilizable compounds therein. Moreparticularly, this invention relates to a method and apparatus for thegeneration of volatile materials which can be achieved in a greatlyreduced time frame as compared with conventional volatile expression orgeneration techniques. The volatiles may be separated or used to enhanceother separations, e.g. in flow-through processes.

BACKGROUND OF THE INVENTION

Grains containing fats and oils have been dried by microwave heatingfollowed by steps to remove husks and to extract oils, as indicated inU.S. Pat. No. 4,464,402, Aug. 7, 1984 (Gannon). The use of microwaveenergy to heat an extractant medium has also been investigated byGanzler & Salgo, 1987, Z. Lebensm Unters Forsch 184: 274-276. In thelatter type of application, most of the microwave energy is absorbed bythe extractant subsequently resulting in the heating of the extractant;accordingly, very little energy reaches the inner parts of the materialto be extracted.

Plant material has been exposed to microwave energy in an air stream toproduce headspace-like samples of volatile material as documented byCraveiro et al., 1989, Flavour and Fragrance Journal 4: 43-44. Nodocumentation has been compiled in terms of the ability to generatevolatiles in a dynamic mode, such as those produced by purge and trapmethods, and further no novel apparatus therefor has been set forth.

Canadian Patent No. 987,993 issued to Heitkamp et al., describes amicrowave-induced migration of flavours and aromas to the surface ofmaterials, such as tobacco or tea, in the presence of moisture andoptionally, a solvent. In U.S. Pat. No. 5,002,784, Pare et al., teachthat biological materials containing microwave absorbing substances,which are subjected to microwave radiation while in contact with anextractant microwave transparent or partial transparent, results indifferential heating of the material to be extracted. The latter effectsa disruption of the inner glandular and vascular systems of the materialand causes a very rapid selective extraction of a variety of naturalproducts.

The prior art fails to recognize the usefulness of microwave generationof volatile components from a matrix containing the same, followed byprocessing of the residual matrix. Further, the prior art is deficientin terms of any teaching pertaining to the disruption of the equilibriumbetween the liquid or solidphase containing the volatilizable componentsand the gaseous phase containing volatilized components or any apparatuscapable of effecting the latter.

SUMMARY OF THE INVENTION

The present invention is directed to solving these deficiencies andfurther provides an apparatus which may be associated with otheranalytical devices, e.g. supercritical fluid and gas or liquidchromatography instruments, during the process of generating thevolatilizable components.

The need for a general method to generate volatiles both, in a static,and in a dynamic mode, and an apparatus therefor which can be used for avariety of sources or origins, is well recognized. The fragrance, foodand environmental industries, in particular, require methods andapparatus that are versatile, relatively inexpensive to operate and thatdo not involve intricate operations that increase the risks of sampleloss and sample contamination.

The extraction industry, the petroleum industry, the health and safetyindustries associated with emergencies such as those related to chemicalspills, in particular, require methods that are versatile with respectto the substance(s), to be selected, relatively inexpensive, simple andsafe to operate to minimize the hazards associated with the generationand subsequent handling of substances under that particular state.

In accordance with aspects of the present invention, protocols for thegeneration .of volatiles from any liquid or solid matrix can beperformed (more easily and with greater efficiency and expediency; suchadvantages additionally permit less error and less contaminationpossibilities) when a microwave applicator is used to enhance thevolatility of substances that are present in the matrices and,optionally, to disrupt the equilibrium between the liquid or solid phaseof the matrix and the resultant gaseous phase from the volatilization ofthe substances. This procedure may be performed in a closed container soas to bring the chemical composition of the gaseous phase similar oridentical to that present originally in the liquid or solid phase, oroptionally, to bring one or all of the substances to a supercriticalstate.

One object of the present invention is to provide a process forgenerating volatiles or supercritical fluid material from any liquid orsolid matrix by the steps comprising: (a) providing volatiles in asubdivided form within a liquid or solid matrix and comprising one ormore substances contained in a closed container or the like; (b)exposing the subdivided material, while within the solid or liquidmatrix, to microwave radiation and disrupting the equilibrium betweenthe solid or liquid phase and the gaseous phase in favour of the gaseousphase without physically removing the volatiles, until substantialvolatilization of the material has occurred; (c) subsequently separatingthe thus created gaseous phase from the solid or liquid phase whilestill in the same container, or in another container connected thereto,and optionally; (d) recovering the gaseous phase from the same containeror another container connected thereto; or optionally (e) exposing thesubdivided material to microwave radiation until sufficient energy hasbeen imparted to bring the material to its supercritical state.

In the above process, and in some cases, the volatiles can be used inapplications where their isolation is not required.

Further, where it is desirable to obtain volatiles in the gaseous phasein a relative concentration so as to be similar or substantiallyidentical to that originally present in the solid or liquid phase, themicrowave irradiation in step (b) is maintained for a sufficiently longperiod to effect a disruption of the equilibrium normally presentbetween the gaseous, and the solid or liquid phase, so as to impartenergy preferentially to the liquid or solid phase thus resulting in thegeneration of volatiles in the gaseous phase in the desired proportions.

Preferably, Where the desired substances are readily amenable toestablished analytical protocols, for example, a chromatographicseparation coupled to an appropriate detector, the gaseous phase arisingfrom the microwave treatment is delivered directly into the selectedanalytical device(s) using the apparatus described herein.

Still further, where the desired components are in trace amounts withrespect to other substances of relatively different volatility, theinvention may be employed in such a manner as to effect the selectiveand successive volatilization of the various substances. It will beapparent to those skilled in the art that the order in which thecomponents will be volatilized will be determined by the characteristicsof the components, namely, the vapor pressure and the dielectricconstant.

The microwave dose should be chosen to maximize the volatilization ofthe desired components, or the conversion to the supercritical state ofthe desired substance, in a minimal amount of time, without affectingthe nature of the components and by selecting appropriate operatingparameters based on the nature of the components. The absolute value ofthe dielectric constant, the heat capacity, the enthalpy of formation,the ionization energy being some of the essential characteristics forthis process.

Yet another object of this invention is to provide a method forexpressing volatilizable components from a liquid or solid matrixcontaining the volatilizable components, comprising: providing a matrixhaving volatilizable components dispersed therein; exposing the matrixto microwave energy to effect volatilization of at least one of thevolatilizable components; and separating at least one volatilizedcomponent from the matrix.

In addition to the foregoing, there is a need for a method of enhancingthe volatility of substances present in a matrix having volatilizablecomponents which permits disruption of the equilibrium between theliquid or solid phase of the matrix and the gaseous phase that resultsfrom the volatilization, to thereby establish a product which has achemical composition, in terms of its gaseous phase, which issubstantially similar or identical to that present in the originalmatrix.

A further embodiment of the present invention satiates theaforementioned need and provides., as a further object of the invention,a method of selectively separating volatilizable materials from a liquidor solid matrix containing the volatilizable materials comprising:providing a matrix selected from a solid or liquid, the matrix havingvolatilizable materials dispersed therein; enclosing the matrix within acontainer, the container having a selectively permeable membraneassociated therewith, the membrane adapted to selectively pass at leastone of the volatilizable materials when volatilized; exposing the matrixto microwave energy to effect volatilization of at least one of thevolatilizable components in the matrix; and passing at least onevolatilized component through the membrane.

As volatility is a physical characteristic specific to a given compound,selectivity of expression for volatilizable compounds contained within agiven matrix for selective removal, is desirable. Such removal reducesthe likelihood of expressed compounds containing contaminants andresults in a generally more efficient expression protocol.

The present invention addresses the favourable technique outlined aboveand another object of the present invention, is to provide a method ofsequentially separating volatilizable components from a matrixcontaining the components each having a different volatility, theimprovement comprising the steps of: providing a matrix havingvolatilizable materials dispersed therein; enclosing the matrix within acontainer, the container having a selectively permeable membraneassociated therewith, the membrane adapted to selectively pass throughat least one of the volatilizable materials when volatilized; exposing,in a first exposure step, the matrix to a microwave applicator at afirst energy intensity to effect volatilization of at least one of thevolatilizable components; removing at least a first volatilizedcomponent; exposing, in a second exposure step, the matrix to themicrowave applicator at a second energy intensity to effectvolatilization of at least one of the volatilizable components remainingin the matrix.

The invention includes a method of improving flow-through separationsfrom a matrix having a microwave-absorbing liquid component, the stepsincluding exposing a flow of the matrix to microwave radiation treatmentto vaporize microwave-absorbing liquid;

processing the vapor in one of the following two ways:

i) flowing the vapor through a permeable membrane selective therefor andremoving the vapor; and

ii) enclosing the vapor and matrix in a confined space in contact with aseparation medium and flowing treated matrix through this separationmedium to separate a component; and

recovering the residual matrix.

Of particular interest are continuous flow embodiments where themicrowave-induced vaporization is continuous or continual.

Another aspect of the invention covers a method of rendering a solid orliquid matrix containing a preferentially microwave-absorbing liquid anda component to be analyzed or processed, more suitable for such analysisor processing, the method including exposing the matrix to microwaveenergy to vaporize at least one microwave-absorbing liquid;

passing a vaporized liquid through a selective permeable membrane toseparate a vaporized component before the matrix is heatedsignificantly;

recovering the residual matrix and any residual vapor; and

passing the residual matrix and any residual vapor to means selectedfrom analysis means and processing means.

One preferred example is the vaporization of water and its separationthrough a selective water-permeable membrane. Another is where twovolatiles are generated concurrently with only one being separatedthrough a selective permeable membrane. In preparing mixtures for liquidchromatography it is desired to remove water (or any polar liquid thatboils at a temperature below water), and according to this example wateris removed as vapor through a water-selective membrane. Another exampleis where a moist solid matrix is treated to remove water as vapor, andthe dry matrix is further processed e.g. by eluting an analyte into anon-aqueous solvent, or into an elevated temperature gas flow.

A further aspect involves a method of increasing the rate of filtrationof a liquid matrix through a filter able to separate a relativelynon-microwave-absorbing component of the matrix, the matrix including amicrowave-absorbing liquid, this method involving exposing the liquidmatrix to microwave radiation to vaporize the microwave-absorbing liquidin a confined space upstream of the filter thereby generating a pressureagainst the filter surface; and

maintaining the pressure by continued microwave radiation exposure whilepassing the matrix through the filter to generate a filtrate.

In one preferred aspect a water-based matrix is treated, with only partof the water being vaporized. The amount of microwave energy used can beadjusted to control the pressure to a desired range.

The invention further includes an apparatus for the removal of amicrowave-absorbing liquid from a matrix containing the liquid in aflow-through manner, having an elongated vessel having an inlet and anoutlet and adapted to contain a flow of the matrix;

a microwave inlet adapted to feed microwave radiation into the vesselnear the inlet end;

a selective permeable membrane in a wall portion of the vesseldownstream of the microwave inlet;

a vented or vacuum-subjected enclosure surrounding the membrane; and

means to feed matrix into the inlet of the vessel.

The invention includes also an apparatus for separating a separablecomponent from a liquid matrix having a microwave-absorbing liquidcomponent, including a vessel having an inlet and an outlet with anoutlet zone just upstream of the outlet;

a substantially non-deformable separation medium extending across thevessel just upstream of the outlet zone;

the vessel inlet being positioned to introduce the liquid matrixupstream of the separation medium;

the vessel providing for a liquid zone to be spread over the separationmedium and a vapor zone to be spread over the liquid zone; and

a microwave inlet positioned to direct microwave radiation into theliquid zone.

Having thus generally described the invention, reference will now bemade to the accompanying drawings illustrating preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an apparatus to effect the separation ofvolatiles, and subsequent direct transfer of the volatiles into anotherdiscrete unit;

FIG. 2 is a comparison of the gas chromatograms of the volatilesobtained from conventional headspace analysis (top trace-labelledheadspace) and from this invention (bottom, inverted trace-labelledMAP);

FIG. 3 is a diagram of a flow-through apparatus to separate amicrowave-absorbing liquid as vapor from a matrix before analysis orfurther processing; and

FIG. 4 is a diagram of a flow-through apparatus to utilize in situmicrowave-generated vapor to pressurize liquid at the surface of aseparation medium and increase flow rate through the medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The mechanism of action of this volatile generation process has beeninvestigated using a variety of matrices and conventional sorbents totrap the volatiles evolved. The volatiles were monitored in comparisonto those obtained when conventional methods were applied to identicalmatrices.

These investigations led to the conclusions that the microwave-assistedprocess proceeds generally as set forth herein. The microwave raystravel freely through the container (selected from those materialspartially transparent to microwave rays) and reach the matrix. Thematrix is made up of more than one component, each of which possessescharacteristic physical properties and, more particularly, dielectricconstant and a characteristic vapor pressure. The relative abilityexhibited by each of the components to absorb the microwave rays isdependent upon the absolute value of their respective dielectricconstant. Generally, components, such as water, possess a largedielectric constant at room temperature and therefore absorb to a greatextent the microwave rays. The absorption of the microwave rayssubsequently results in the heating of such compounds.

It is possible to control the power of the applied microwave rays so asto ensure an overall heating rate that is constant for each component asthe heat so-generated is diffused passively to all of the componentsthroughout the matrix. The rate of volatilization of each component,within a given matrix, is dependent upon the respective vapor pressurethereof. Water, for example, has a lower vapor pressure than benzene,hence benzene will volatilize more rapidly, at a given temperature, thanwater, thus a net effect of volatilizing the benzene preferentially tothe water.

Under conventional steady state heating such as that applied by othertechnologies, such as conventional headspace analysis, the relativeconcentration of the volatiles in the gaseous phase is at substantialequilibrium with that in the solid or liquid phase of the matrix and isdependent upon the partial vapor pressure of each component;accordingly, the relative concentration of a given component in the gasphase is not equal to that while in the solid or liquid phase. Thisposes difficulties during analysis and specifically upon an attempt toquantify a material dispersed in a matrix.

Furthermore, the absolute value of the dielectric constant of a givensubstance decreases when the substance reaches the gas phase, e.g.liquid water has a dielectric constant of about 80 at 293° K. whilesteam, at 373° K., has a value of about 1. Hence, almost all of theapplied microwave energy is used to selectively heat the liquid or solidphase of the matrix. Moreover, the capacity of a substance to absorbenergy while resisting a temperature increase is dependent upon the heatcapacity of the substance. As an example, the temperature of 1 gram ofwater is elevated by only 1° K. when the same absorbs 1 calorie ofenergy at 293° K.

Having regard to the above, the present invention makes it possible toeffectively apply a controlled amount of microwave energy that willselectively heat the liquid phase at a temperature such that thevolatiles are maintained in the gaseous phase without volatilizing thenon-volatiles. This permits the application of more energy into thematrix to disrupt the phase equilibrium that normally prevails betweenthe gaseous phase and the solid or liquid phase of the matrix as theenergy is preferentially absorbed by the liquid, or solid, fraction ofthe system over the gaseous fraction. Under such conditions, it ispossible to generate volatiles into the gas phase so that their relativegaseous concentration is substantially equal to that which they had inthe liquid or solid state. This aspect of the invention relates to thegeneration of volatiles in a purge and trap fashion.

In a further embodiment of the present invention, the gaseous phase canbe separated from the liquid or solid phase of the matrix, whileenhancing the rate of volatilization, by incorporating the use of anappropriate selectively or semi-permeable membrane that allows the flowof gaseous materials in one direction (away from the matrix) whilepreventing the flow of liquid or solid materials. The functional use ofsuch membranes will be well-known to those skilled in the art and thereare several known types which are used for given bands of selectivity.Preferably, but not exclusively, a membrane that does not allow thepassage of water, whether in a liquid or a gaseous state, is appropriatefor direct transfer of the volatiles onto an inlet port of an analyticaldevice such as a gas chromatograph. FIG. 1, as described hereinafter,depicts a typical apparatus for this purpose.

In another configuration of this invention, a protocol can be designedto generate supercritical fluids from a variety of materials, waterbeing of particular interest. The dielectric constant of water is about80 at 293° K. At its boiling point, namely 373° K., water has adielectric constant of about 55 whereas steam has a dielectric constantof about 1. Thus, it is possible to heat all of the liquid phase priorto heating the gaseous phase. In a closed container, the temperature andthe pressure will rise until the supercritical state is reached. Waterexhibits a heat capacity of 1 cal per gram per degree Kelvin at roomtemperature. Once it reaches the supercritical state, water exhibits aheat capacity that goes to infinity. Thus, by employing the presentinvention, it is possible to apply enough energy to effect theconversion of liquid water into supercritical water and to maintain itat that state while providing a given level of microwave energy. Theresulting supercritical water can be used in other applications, as isthe case for supercritical water generated by other technologies. Whilewater is used only as an example, it will be understood that theinvention is not limited to water as will be evident to those skilled inthe art.

In one preferred configuration of the present invention, an apparatus isprovided so that such a membrane is allowed to establish a tight seal inthe container enclosing the matrix of interest. The microwave power isapplied and as the volatiles generation is effected, the membrane may bemoved down toward the matrix so as to reduce the headspace volume abovethe matrix and the membrane. The semi-permeability of the membraneeffects separation as the volatiles are not able to return to the liquidor solid phase. The rate of heating will allow for headspace type ofexperiments, or if disruption of the equilibrium is effected by applyingextra power, then the method will lead to the generation of purge andtrap-like experiments. The membrane can also be retracted to itsoriginal position thus compressing the volatiles into a smaller volume.

The apparatus, as generally set forth in FIG. 1, is particularlywell-suited for interfacing directly onto the injector port, or otherappropriate inlet mechanisms, of an appropriately selected analyticalinstrument, such as a gas, liquid or supercritical fluid chromatographicinstrument. Such an arrangement, by opening of an appropriate valve,allows for on-line transfer of the gaseous volatile materials wherebyone can effect a totally automated analytical protocol for headspace orpurge and trap types of analysis with a single instrument, an option notavailable with any other current technology. The separation methodsmentioned above were noted only for example purposes and it will beunderstood that they are not exhaustive nor limiting with respect toother applications of the process and apparatus, to other methods.

The sample used was water contaminated with west Texas sour crude oil ata concentration of 5 parts per million. Headspace analysis carried aftera 30-minute incubation period at 358° K. while the analysis of thevolatiles produced by the methodology of the invention was performedafter a 30-second irradiation period. All analytical procedures wereidentical.

FIG. 1 illustrates one form of one aspect of the apparatus. As thevolatiles are generated, a mobile semi-permeable or selectively membrane18 disposed within container 10, moves in response to increasing gaseouspressure and then separates the newly generated gas phase from theliquid or solid phase matrix beneath the membrane 18, generallyillustrated in dashed lines. Volatiles passing through membrane 18 exitthe container 10 via conduit 20. Volatiles travelling through conduit 20may be sampled by opening valve 22 for discharge through sampling line24. The volatiles may additionally be forwarded to analysis means 26,which may comprise any known analysis apparatus, e.g. a gaschromatograph, I.R. spectrophotometer, N.M.R. apparatus, massspectrometers, U.V. analysis means, etc.

FIG. 3 illustrates one form of an apparatus for the removal ofmicrowave-absorbing liquid from a matrix. A flow of liquid or solidmatrix proceeds through conduit 2 past microwave inlet 3 where thematrix is exposed to microwave radiation selected to volatilize at leastone microwave-absorbing component (shown as vapor pocket or bubble 8).These bubbles flow against or migrate to selective permeable membrane 4,pass through the selective membrane into enclosure 5 which may be ventedor subject to a vacuum through line 6. The flow rate past the membranecan be slow enough to allow substantially complete separation of thevolatiles: this slow flow rate is enhanced by constriction 10 beforeresidual matrix exits at 7. In FIG. 3 one alternative is shown at 9where a second liquid is volatilized by the microwave radiation but doesnot exit through membrane 4 and continues through exit 7 as pockets orbubbles 9 for subsequent separation e.g. as analyte.

FIG. 4 illustrates one form of an apparatus for separation (e.g.filtration) of a liquid suspension or liquid mixture. The liquid matrixenters through conduit 11 and one-way valve 12. The matrix enters vessel18 near separation (e.g. filter) medium 13 and forms a liquid reservoir14 against medium 13. Microwave radiation inlets are shown at 17 and aresited to direct selected radiation into liquid reservoir 14 to causevaporization of microwave-absorbing liquid. The microwave-generatedvapor is shown at 15 and exerts pressure against liquid 14 and thusagainst separation medium 13 and one-way valve 12. This in situmicrowave-induced pressure is effective to increase flow of matrixthrough medium 13 into collector 19 and hence to exit 20. A vent 16 isshown to facilitate control of pressure. In a preferred mode, thepressure is allowed to increase until most of the liquid in reservoir 14passes through medium 13, and then pressure released through vent 16.Fresh matrix then is introduced through conduit 11 and valve 12 and thecycle repeated.

In the embodiment shown in FIG. 3, the conduit 2 may take the form of apipe or tube, or have a square, rectangular or other non-circularcross-section. The membrane 4 may form an upper portion (arc) or thecomplete circumference (annular) of a section of the pipe or tubeconfiguration. In the latter case, the liquid matrix may be caused toswirl in the membrane region to increase exposure of pockets or bubbles8 to the membrane. In the case of non-circular cross-section conduits 2,the membrane usually will take the form of a band across an uppersurface downstream of the microwave inlet 3, this inlet 3 beingsubstantially coextensive with the membrane band. The enclosure 5 willtake the appropriate form to cover membrane 4.

In the embodiment in FIG. 4, conduit 11 may enter vessel 18 at anylocation, preferably so as to release fresh liquid matrix close to thesurface of separation medium 13. In this pressure-enhanced separationembodiment, the vessel 18 may be configured as a rigid pipe andseparation medium 13 as an annular concentric form within the pipe.Preferably separation medium 13 is supported against a rigid poroussupport (not shown). The vessel 18 (e.g. pipe) may be selected to betransparent to the microwave or the microwave inlets may be designed toaccess through appropriate regions. The liquid matrix will flow throughthe annular space between the pipe and medium and be subject to themicrowave radiation. On vaporization of liquid, pressure will begenerated in this annular space and will be directed by the rigid pipeagainst the separation medium to enhance flow through this medium. Toprevent the pressure from being dissipated axially before the desiredflow through the medium is achieved, it may be desirable to positionvalvest gates or constrictions to confine the pressure within theannular space surrounding the separation medium in the region where themicrowave radiation is applied. Thus it is preferable to pass liquidmatrix into this region intermittently and to cycle the microwaveradiation/pressure appropriately. After separation the treated matrix orfiltrate will exit at one or both ends of the medium annulus. Theseparation medium can be any solids-retaining medium, or any liquid- orsolute-selective membrane. Various filter media, liquid permselectivemembranes or reverse osmosis membranes may be used.

Examples of the invention are provided below wherein microwaveradiation-induced volatile generation was used. Disruption of theequilibrium normally present between liquid or solid substances andtheir gaseous state as described demonstrate improvements in one or moreaspects. These aspects include yield, sensitivity, number of volatiles,identity of volatiles, reduced time and production costs (reducedoperational costs and reduced capital costs), reduced number ofoperations and reduced process-related hazards (to humans and to sampleintegrity), or a combination thereof, over the conventional headspaceand purge and trap processes currently used. These examples areillustrative and typical, but are not to be considered exhaustive orlimiting.

EXAMPLE 1

As a representative example of headspace analysis, the volatiles from awater sample contaminated with a crude oil were obtained from aconventional headspace sampler and from this invention. Water wascontaminated with some west Texas sour crude oil at a concentration of 5parts per million. Two 10 mL aliquots were transferred into twoidentical 20 mL vials that were sealed hermetically. The first vial wasthen subjected to a 30-minute incubation period at 358° K. on aconventional, commercially available, headspace sampler (Hewlett Packard19395A). A 1-mL volume of the resulting headspace was injected directlyinto the injector port of a gas chromatograph (Hewlett Packard 5890Series II, flame ionization detector) equipped with an appropriatecolumn to effect the separation and the resolution of the volatiles(HP-1, 25 meters, 1 micrometer thickness).

The second vial was subjected to the process taught by this invention,namely by exposure to microwave radiation (2450 MHz, 650 Watts) for 30seconds. A 1-mL volume of the resulting headspace was injected directlyonto the injector port of a gas chromatograph under the same conditionsas per the conventional headspace sampler.

FIG. 2 shows the two resulting traces recorded under identicalconditions, both scales being the same. This example demonstrates thatthe methodology of the present invention yielded more volatiles, interms of their overall absolute quantity, in a much reduced samplingtime. Furthermore, this example also shows that the use of thisinvention led to the detection of more components, principally for themore volatile substances, hence an evidence that the excess energyapplied to the system was absorbed selectively by the liquid phase overthe gaseous phase.

EXAMPLE 2

Fresh sage, of 80% moisture content, obtained fromSaint-Jean-sur-Richelieu, Quebec, Canada, was chopped coarsely intopieces and subjected to conventional purge and trap analysis as well asto conventional headspace analysis. A portion of the same material wasinserted into a container. The container was sealed by a cover throughwhich an orifice had been made. A commercially available sorbent, in anappropriate container, was fitted from the inside of the container tothe orifice thus creating an hermetic seal. The container and itscontents were then treated by exposure to microwave radiation for 90seconds so as to severely disrupt the equilibrium that existed betweenthe solid plant material and the gases around it. The sorbent was theneluted and the eluate analyzed by gas chromatography. The results of theanalysis evidenced the presence of volatile terpenoids as well as lessvolatile ones.

A typical analysis contained 4-carene, alpha-thujene, alpha-pinene,camphene, 2-beta-pinene, sabinene, beta-myrcene, 1,8-cineole,beta-phellandrene, alpha-terpinolene, alpha-thujone, beta-thujone,camphor, bornyl acetate, cis-caryophyllene, and alpha-caryophyllene.This analysis compared favourably to the purge and trap analysis, whilebeing superior to the headspace analysis, the latter lacking some of thelesser volatile compounds (sesquiterpenoids).

It will be evident to those skilled in the art that the choice ofsorbent is dependent upon the nature of the volatiles of interest (inthe present example, a silica sorbent was appropriate). Direct injectionof the volatiles without the use of any trap of any kind (cold orsorbent) is possible by the use of this invention because of the shortsampling duration and because of the relatively small volume of samplingnecessary. Purge and trap would not allow such a direct injectionwithout a cold trap of kind, or of a sorbent. The use of this invention,in this particular example, showed that a purge and trap analysis can beperformed more rapidly, with less operations (hence reduced risks ofsample loss or sample degradation), at a much reduced cost and with lessenergy than conventional technology. Again, the use of this inventionrequires less intricate equipment occupying a much reduced space andobtainable at a much reduced capital cost.

EXAMPLE 3

As a representative example of headspace analysis of a solid matrix, thevolatiles from a soil sample contaminated with a crude oil were obtainedfrom a conventional headspace sampler and from this invention. The soilwas contaminated with west Texas sour crude oil at a concentration of4.28 parts per million. Two 1.0 g aliquots were doped with 0.5 mL ofwater and were transferred into two identical 20 mL hermetically sealedvials. The first vial was subjected to a 30-minute incubation period at358° K. on a conventional, commercially available, headspace sampler(Hewlett Packard 19395A). A 1-mL volume of the resulting headspace wasinjected directly into the injector port of a gas chromatograph (HewlettPackard 5890 Series II, flame ionization detector) equipped with anappropriate column to effect separation and resolution of the volatiles(HP-1.25 meters, 1 micrometer thickness).

The second vial was subjected to the process according to the presentinvention, namely by exposure to microwave radiation at a frequency ofand a power rating of 650 Watts for 30 seconds. A 1-mL volume of theresulting headspace was injected directly into the gas chromatographunder the same conditions as per the conventional headspace sampler.

The results obtained through this example demonstrate that the sample,when treated according to the present invention, yielded more volatiles,in terms of their overall absolute quantity, in a substantially reducedsampling time and that the nature of the volatiles is exactly identicalto that obtained by conventional technology. Furthermore, this examplealso evidences that the excess energy applied to the system was absorbedselectively by the solid (and small amount of liquid) phase over thegaseous phase.

EXAMPLE 4

This example relates to headspace analysis in the biomedical andforensic fields and indicates usefulness in alcohol detection from anaqueous sample.

The detection of alcohol from an aqueous sample was performed on aconventional headspace sampler and by using the methodology of thepresent invention. Water was spiked with ethanol at a concentrationvarying between 0.8 to 80 mg per 100 mL. Two 10 mL aliquots weretransferred into two identical 20 mL hermetically sealed vials. Thefirst vial was then subjected to a 30-minute incubation period underconditions set forth in Example 3. A 1-mL volume of the resultingheadspace was injected directly into the injector port of a gaschromatograph equipped with an appropriate column to effect theseparation and the resolution of the volatiles, these apparatus beingthose indicated in Example 3. The second vial was subjected to theprocess taught by this invention, namely by exposure to microwaveradiation (2450 MHz, 650 Watts) for 30 seconds. A 1-mL volume of theresulting headspace was injected into the injector port of a gaschromatograph under the same conditions as per the conventionalheadspace sampler. An identical experiment was performed by substitutingwhole cream (35% fat) to water, cream being a most challenging matrixwith which to work. The results of this example demonstrate that thisinvention was more sensitive by a factor of at least 2, required a muchreduced sampling time, and provided for the detection of more species(in the case of the cream).

The overall reduction in analysis time evidenced in this example is ofextreme importance to forensic and biomedical applications such as thedetermination of the ethanol content in blood for drivers suspected tobe under the influence of alcohol and for the monitoring of dissolvedgases in blood of patients undergoing surgery. Again, the example alsoshows that the use of the invention allowed the excess energy applied tothe system to be absorbed selectively by the liquid phase over thegaseous phase.

EXAMPLE 5

This example describes one gas-phase extraction method for the headspaceanalysis of volatile organic compounds, often referred to as VOCs, inwater, and compares the results to those obtained by conventional staticheadspace analysis in terms of sensitivity, linearity, precision, andsample preparation time.

A 10-component purgeable aromatics standard solution (2.0 mg/mL of eachcomponent in methanol; components being benzene, toluene, ethylbenzene,chlorobenzene, o-, m-, and p-xylenes, and 1,2- 1,3 and1,4-dichlorobenzenes, Hewlett-Packard Part No. 8500-6080, Method 8020)was diluted to 1, 4, 20, 100 and 500 ppm with methanol. A series of10-mL water samples, contained into 20-mL headspace vials, were spikedat 10, 40, 200, 1000, and 5000 ppb of each component by adding 100-μLaliquots of the diluted solutions (Drummond fixed volumesmicro-pipette). Blanks consisted of 10-mL water samples that were spikedwith one 100-μL aliquot of methanol alone and they were used to monitorthe potential interferences arising from the solvent. All samples werecapped within five minutes form the end of the spiking procedure andwere left to stand for at least 24 hours before the experiments wereperformed.

A microwave oven was used to apply the microwave energy to the samplesfor microwave treatment (microwave assisted process, MAP™) gas-phaseextraction experiments. The power level was kept low to minimize theover-pressurizing of the headspace vials and the potential for lossesdue to leaks or the potential for explosion. A wide range ofexperimental conditions were investigated. The results reported in thisexample were obtained under the following conditions: Extraction:Microwave power 500 W: Frequency 2450 MHz; Irradiation and spinningcycle of 15 s irradiation, 5 s of spinning, 15 s of irradiation and 5 sof spinning (total sample preparation time of 40 s); Sampling: Samplingwas effected by using a headspace sampler (Hewlett-Packard 7694)operated with a loop temperature of 90° C.; Transfer line temperature of100° C.; Vial pressurization time of 0.2 min.; Loop fill time of 0.2min.; Loop equilibration time of 0.05 min.; and sample injection time of0.4 min. (equilibration time of 0 min.). The headspace sampler wasfitted with a 0.5 m heated transfer line. All experiments were performedseveral times and triplicates were run at each occasion.

The resulting headspace was analyzed using a Hewlett-Packard gaschromatograph 5890, Series II Plus, equipped with a split-splitless SSinlet and a flame ionization detector. An HP-5, 30 m×0.32 mm i.d. fusedsilica column capillary column with a film thickness of 1.0 μm, wasused. Operating conditions were as follows: Inlet temperature 250° C.;Detector temperature 250° C.; Temperature program 60° C. for 0.5 min.,60° C. to 120° C. @10° C./min., held at 120° C. for 3.5 min (total runtime of 10 min.); Helium carrier gas at 2 mL/min.; constant flow mode (8psi at 60° C.); Sample loop of 1.0 mL, split flow of 20 mL/min. (1:10split ratio); Headspace vial pressurization maintained at 22 psi via thechannel D of the HP 5890 electronic pressure control unit.

For comparison purposes, static headspace sampling experiments wereperformed using the same headspace sampler. Optimized operatingconditions for the matrix of interest were as follows: Extraction: Oventemperature at 80° C.; Vial equilibration time of 30 min.; Agitation atmaximum (setting 2); Sampling and gas chromatographic analysis: Exactlyas per the microwave gas-phase experiment above. All experiments werealso performed several times and triplicates were run at each occasion.

Tables 1 and 2 provide precise information about the sensitivity, thelinearity, and the reproducibility data obtained from both methods. Bothmethods were characterized by regression coefficients greater than0.9999. The analytes sensitivity, however, was significantly better forMAP gas-phase extraction with response signals greater by circa 35% foreach component at each concentration. The relative standard deviation,that included the total systemic error factor, was also better for theMicrowave Treatment with an overall value of 1.4% (between 0.19% and2.3%) whereas that of conventional static headspace was at 2.3% (between1.3% and 3.3%).

The greater sensitivities obtained are the result of the microwaveenergy being imparted more selectively to the water because the latterabsorbs microwaves preferentially to the surrounding gaseous medium.This energy is then released to the neighbouring low-absorption species(volatile organic compounds, VOCs) which are, in turn, vaporizedselectively and rapidly in proportions that are related to their vaporpressure and to their heat capacity.

                  TABLE 1                                                         ______________________________________                                        Linearity data (from gas chromatography-flame ionization detector             results) for 30-minute conventional status headspace and 40-                  second Microwave Treatment gas-phase extractions of volatile                  organic compounds (VOCs) in water                                             Regression Data                                                                             Headspace                                                                              Microwave Treatment                                    ______________________________________                                        Multiple R    0.99999  0.99999                                                R Square      0.99998  0.99999                                                Adjusted R Square                                                                           0.99997  0.99999                                                Standard Error                                                                              9336     7390                                                   ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Comparative sensitivity and reproducibility data (from gas                    chromatography-flame ionization detector results) for                         conventional 30-minute static headspace sampling and 30-second                Microwave Treatment gas-phase extraction of volatile organic                  compounds (VOCs) from water                                                                                      Microwave                                                        Microwave    Treatment/                                 Concen- Headspace     Treatment    Headspace                                  tration Response RSD*     Response                                                                             RSD*  Ratio                                  ______________________________________                                        10   ppb     9830    3.30    12860 2.18  1.31                                 40   ppb     35600   3.21    47869 2.30  1.34                                 200  ppb    178100   1.62    241021                                                                              1.50  1.35                                 1,000                                                                              ppb    853516   2.11   1194101                                                                              0.19  1.40                                 5,000                                                                              ppb    4348711  1.29   5892204                                                                              0.79  1.35                                 ______________________________________                                         *Relative Standard Deviation                                             

Microwave Treatment gas-phase extractions make use of physicalphenomena, that are fundamentally different from those applied inconventional sample preparation techniques. It provides for dramaticreduction in the preparation time required per sample--here from 1800 to40 seconds, a factor of 45. In addition, in the analytical examplepresented herein, microwave treatment gas-phase extraction also offerssignificant advantages over static headspace in terms of sensitivity,while offering better reproducibility and similar characteristics. Itwill be evident to those skilled in the art that the dramatic reductionin sample preparation time, on a per sample basis, along with therelative ease of rapidly implementing widely varying operatingparameters are attributes of choice for methods to be used during fieldanalytical activities.

EXAMPLE 6

This example describes one microwave treatment gasphase extractionmethod for the headspace analysis of volatile organic compounds, oftenreferred to as VOCs, in soils, and compares the results to thoseobtained by conventional static headspace analysis in terms ofsensitivity, linearity, precision, and sample preparation time.

A 7-component purgeable aromatics standard solution (components beingbenzene, toluene, ethylbenzene, chlorobenzene, and 1,2-, 1,3 and1,4-dichlorobenzenes) in methanol was used to spike 1-gram naturalagricultural soil samples contained into 20-mL headspace vials at 1, 10,0.25, 0.50, 1.00, 2.50 and 5.00 ppm. Blanks consisted of 1-gram naturalagricultural soil samples that were spiked with an aliquot of methanolalone and used to monitor the potential interferences arising from thesolvent. All samples were capped within five minutes from the end of thespiking procedure and were left to stand for at least 24 hours beforethe experiments were performed.

A microwave oven was used to apply microwave energy to the samples formicrowave treatment gas-phase extraction experiments. The power levelwas kept low to minimize the over-pressurizing the headspace vials andthe potential for losses due to leaks or the potential for explosion. Awide range of experimental conditions were investigated. The resultsreported in this example were obtained under the following conditions:

Extraction: De-capping of vial, addition of a 2-mL aliquot of water andrecapping of the vial; Microwave power 500 W; Frequency 2450 MHz;Irradiation and spinning cycle of 20 s irradiation, 5 s of spinning, 20s of irradiation and 5 s of spinning (total sample preparation time of50 s); Sampling: Sampling was effected by using a headspace sampler(Hewlett-Packard 7694) operated with a loop temperature of 90° C.;Transfer line temperature of 100° C.; Vial pressurization time of 0.2min.; Loop fill time of 0.2 min.; Loop equilibration time of 0.05 min.;and sample injection time of 0.4 min. (equilibration time of 0 min.).The headspace sampler was fitted with a 0.5 m heated transfer line. Allexperiments were performed several times and triplicates were run ateach occasion.

The resulting headspace was analyzed using a Hewlett-Packard gaschromatograph 5890 Series II Plus, equipped with a split-splitless SSinlet and a flame ionization detector, An HP-5, 30 m×0.32 mm i.d. fusedsilica column capillary column with a film thickness of 1.0 μm, wasused. Operating conditions were as follows: Inlet temperature 250° C.;Detector temperature 250° C.; Temperature program 60° C. for 0.5 min.,60° C. to 120° C.@10° C./min., held at 120° C. for 3.5 min. (total runtime of 10 min.); Helium carrier gas at 2 mL/min.; constant flow mode (8psi at 60° C.); Sample loop of 1.0 mL, split flow of 20 mL/min. (1:10split ratio); Headspace vial pressurization maintained at 22 psi via thechannel D of the HP 5890 electronic pressure control unit.

For comparison purposes, static headspace sampling experiments wereperformed using the same headspace sampler. Optimized operatingconditions for the matrix of interest were as follows: Extraction:De-capping of vial, addition of 2-mL aliquot of water and recapping ofthe vial; Oven temperature at 80° C.; Via equilibration time of 30 min.;Agitation at maximum (setting 2); Sampling and gas chromatographicanalysis: Exactly as per the microwave gas-phase experiment above. Allexperiments were also performed several times and triplicates were runat each occasion.

Both methods showed good linearity although the overall sensitivity wassignificantly better for microwave treatment gas-phase extraction thanstatic headspace with response signals greater by circa 50%.Furthermore, the conventional headspace methodology was unable to yieldquantitative results for samples spiked at 0.10 and 0.25 ppm as well asfor some components in the 0.50 ppm samples; the microwave experimentson the other hand, were quantifiable from 0.25 ppm onwards.

As it will be clearly understood by those skilled in the art, themicrowave absorbent material, due to the vaporization thereof mayrequire replenishment. Where the absorbent material comprises, forexample, water, the material may be hydrated prior to microwave exposureor may be rehydrated subsequent to treatment.

It will be appreciated by those skilled in the art that the process isapplicable to systems which include a plurality of phases. An example ofsuch a system can be seen in the expression of volatile materials from acapillary sampling tube. The extraction of volatilizable materials fromconventional methods is not only extremely difficult using presenttechnology, but further results in the potential for significant lossesof the material to be extracted. By employing the microwave processaccording to the present invention, extraction or expression of thematerials is substantially complete and results in a substantialreduction in volume losses of the material to be expressed.

EXAMPLE 7

This example is relevant to other currently used disposable analyticaldevices. This application of the invention is related to the extractionfrom natural or synthetic fibres, e.g. hollow fibres used in so-calledsolid-phase micro-extraction applications of compounds, e.g.contaminants, such as, volatile organics from aqueous solutions. Suchfibrous materials are often used as a means to concentrate analytesprior to releasing them into an inlet of an analytical apparatus, e.g.by desorbing them into the inlet of a gas chromatograph.

There is a need to release chemicals from the fibres as rapidly aspossible. To demonstrate the advantages associated with the use of thepresent invention, commercially available hollow fibres were used inso-called solid-phase micro-extraction Supelco. All the fibres werepre-conditioned in the manner prescribed by the manufacturer until thefibres proved to be fee of contaminants. The fibres were then used asprescribed by the manufacturer to effectively sample and concentrate thecontaminants. In this example, BTEX (i.e. benzene, ethylbenzene,toluene, xylenes) were the contaminants found in a water sample. Wateraliquots of similar volumes were used and the sampling time (i.e.immersion of fibre into the water sample) was kept constant. for allexperiments (15 minutes).

Once the sampling time had elapsed, the fibres were cut from theirholders and put into series of two hermetically-sealed 20-mL headspaceanalysis vials. The first vial of the series was then subjected toexposure to heat in a conventional oven at 353° K. for a 30-minuteperiod. A one-mL volume of the resulting headspace was injected manuallyat 498° K. over a 45 second period into the splitless inlet port Of agas chromatograph (HP-5890 Series II), appropriately fitted with a flameionization detector (at 553° K.) and a SPB-1 column (30 m, 0.53 mm i.d.,1.5 μm film thickness). The second vial was treated with a single15-second, 900-watts, 2450 MHz microwave-irradiation period. A one-mLvolume of the resulting headspace was analyzed in a similar manner asthe first vial.

The conventional heating experiments failed to produce any recordabletraces of the contaminants, whereas the microwave-treated samples led torecognizable patterns. To further demonstrate the advantages of thisinvention, more experiments were carried out with other types of sealedcontainer, e.g. 3-mL disposable syringes properly fitted with a 24-gaugeneedle sealed with a teflon disc, 2-mL and 4-mL sample vials, etc. Theresults of these experiments led to the conclusion that the volume ofthe container is an important parameter in the sensitivity of themethod.

It will be evident to those skilled in the art, that the use of theteachings of the present invention with an appropriately designedcontainer, such container being, e.g. an inlet of a given analyticalinstrument, e.g. gas chromatograph, properly fitted with a microwavesource, leads to much faster gas-phase extraction of contaminants fromthe fibres, thus removing the potential need for focusing techniques.Furthermore, it will also be evident to those skilled in the art thatthe use of this invention applies to samples that were collected fromthe liquid phase as well as from the gaseous phase of a solutioncontained into a vial, or collected directly from a gas, or a gaseoussolution, or a gas mixture, be it enclosed or not (e.g. air sampling).

Similar work with difficult to analyze samples, such as potting soils(40 second total preparation time here) were performed and led tosimilar conclusions, namely that the use of this technology allowed forthe quantitation of analytes at much lower levels than is possible withcurrent static headspace technologies. Here again, microwave treatmentgas-phase extractions make use of physical phenomena that arefundamentally different from those applied in conventional samplepreparation techniques. In these particular examples it also providesfor a dramatic reduction in the preparation time required per sample--from 1800 to 40-50 seconds, a factor of 36-45. It will be evident tothose skilled in the art that the dramatic reduction in samplepreparation time, on a per sample basis, along with the relative ease ofrapidly implementing widely varying operating parameters are attributesof choice for methods to be used during field analytical activities.Hence, e.g. coupled to a total organic vapor analyzer, this inventionprovides for unequalled sensitivity performance. The latter attribute isof particular importance in applications where the safety of workers orthat of the general public is involved such as is the case duringcontrolled decontamination work, or during emergency responsesituations, respectively.

In the flow-through separations the selectivity of the membrane orfilter medium can be chosen to allow the passage of the desiredcomponents--as provided for in previous examples--or to allow thepassage of the medium used to dissolve the materials, or, as it will beevident to those skilled in the art, to remove the solvent. Preferredembodiments of this invention include, but are not limited to,enhancement of aqueous solution filtration processes, concentration ofvolatile organic compounds from water for interfacing to gaschromatographic analysis, concentration of organic substances forinterfacing to liquid chromatographic analysis, and as a process to beused with appropriate equipment to remove solvents from solutions--inparticular water--prior to the introduction of the resulting analytesinto a detector means such as an infrared device or a mass detectiondevice such as a mass selective detector, a mass spectrometer, a lightscattering detector or the like, often used in e.g. liquidchromatographic systems.

In the case of solvent removal as liquid e.g. water for example, therate of filtering will be greatly enhanced when submitted to the benefitof this invention as a result of the increase in pressure created by theapplication of microwaves to the aqueous solutions. Furthermore, incurrent use it is necessary to rinse the filter with significant volumesto ensure that all aliquots of the solution have been subjected to thefiltration process. The use of this invention, combined with a judiciousselection of a permeable membrane, will minimize significantly the needto rinse and reduce the possibility of tainting results due to addedcontaminants or introduced sources of interference.

In another embodiment of this invention, the permeable membrane isselected so as to allow the selective passage of the solvent in adynamic mode as vapor. In one particular example, an aqueous solution isallowed to flow through a physical cavity that is equipped with aselective membrane and with means to subject the solution, while in thecavity, to microwave energy. The solution is allowed to flow in thecavity while being exposed to microwaves so as to effect the selectiveheating of the water until the water volatilises at which time it canescape through the membrane while the other constituents continue theirmovement through the chamber and reach an outlet at which point theyexit as an enriched solution or as a mixture of substances devoid ofwater. It will be obvious to those skilled in the art that the presenceor not of water in the material exiting the cavity can easily becontrolled by applying the required amount of energy to effect partialor total volatilisation (can be calculated from the knowledge of theflow rate and the dead volume of the cavity). The use of this inventionwill be of particular interest for applications where it is necessary toconcentrate the contents of analytes which are present in lowquantities, even in ultra-tracequantities during e.g. liquidchromatographic analyses.

It will be obvious to those skilled in the art that this preferredembodiment applies especially well to, although is not limited to, itsimplementation within processes involving chromatographic techniquese.g. gas, liquid, or supercritical fluid chromatography, and detectiontechniques performed under vacuum conditions e.g. mass spectrometer orthat require very low water residue to be effective e.g. Infrareddetector.

It is possible to vaporize part or all of the liquid to be vaporized byadjusting the amount of energy delivered by the microwave generator.Knowing the amount of liquid to be vaporized, its heat capacity andboiling point, one can calculate the amount of energy to be delivered.

The separations can be carried out with a continual flow-through, orwith continuous flow and intervals of minimal flow in which separationproceeds and conditions are adjusted, before another cycle. In thelatter case, the microwave radiation may be interrupted or pulsed foroptimum separations.

Although embodiments of the invention have been described above, it isnot limited thereto and it will be apparent to those skilled in the artthat numerous modifications form part of the present invention insofaras they do not depart from the spirit, nature and scope of the claimedand described invention.

I claim:
 1. A method of improving flow-through separations from a matrixhaving a microwave-absorbing liquid component, comprising:exposing aflow of the matrix to microwave radiation treatment to vaporizemicrowave-absorbing liquid; processing the vapor in one of the followingtwo ways:i) flowing the vapor through a permeable membrane selectivetherefor and removing the vapor; and ii) enclosing the vapor and matrixin a confined space in contact with a separation medium and flowingtreated matrix through this separation medium to separate a component;and recovering the residual matrix.
 2. The method of claim 1, whereinthe matrix flow is intermittent in timed relation with intermittentmicrowave radiation.
 3. The method of claim 1, wherein the permeablemembrane or separation medium is in a form selected from planar andannular.
 4. A method of rendering a solid or liquid matrix containing amicrowave-absorbing liquid and a component to be analyzed or processed,more suitable for such analysis or processing, comprising:exposing thematrix to microwave energy to vaporize at least one microwave-absorbingliquid; passing a vaporized liquid through a selective permeablemembrane to separate a vaporized component before the matrix is heatedsignificantly; recovering the residual matrix and any residual vapor;and passing the residual matrix and any residual vapor to means selectedfrom analysis means and processing means.
 5. The method of claim 4,wherein water is present in the matrix as apreferentially-microwave-absorbing liquid, the water is preferentiallyvaporized by the microwave and the membrane is a selectivewater-vapor-permeable membrane.
 6. The method of claim 4, wherein twoseparate liquids are vaporized, one passes through a selective permeablemembrane and the other is separated in a later step.
 7. A method ofincreasing the rate of filtration of a liquid matrix through a filterable to separate a non-microwave-absorbing component of the matrix, thematrix including a microwave-absorbing liquid comprising:exposing theliquid matrix to microwave radiation to vaporize the microwave-absorbingliquid in a confined space upstream of the filter thereby generating apressure against the filter surface; and maintaining the pressure bycontinued microwave radiation exposure while passing the matrix throughthe filter to generate a filtrate.
 8. The method of claim 7, wherein thematrix is a liquid suspension of solids and the filter is asolids-retaining medium.
 9. The method of claim 7, wherein the matrix isa liquid-liquid mixture and the filter is a liquid-selective membrane.10. The method of claim 7, wherein the matrix is a liquid solution andthe filter is a reverse osmosis membrane.
 11. The method of claim 7,wherein the microwave radiation, pressure build-up and filtrationproceeds in cycles.